Fix floating-point sampling of YUV formats.
Fix floating-point sampling of YUV formats.

Bug b/38268007

Change-Id: I5a75b7ea475848739ca5f3717e2b42c89088dafb
Reviewed-on: https://swiftshader-review.googlesource.com/9828
Tested-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Reviewed-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>

bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,google/swiftshader,bkaradzic/SwiftShader